The present invention relates to a high-definition (HD) television receiver, and more particularly, to a data segment sync signal detector for an HDTV.
There have been carried out many studies on HDTV. Grand Alliance HDTV system specification, a standard for USA HDTV transmission method, was announced on Feb. 22, 1994.
According to this grand alliance HDTV system specification, error control coding is performed on video data for the purpose of transmitting/receiving compressed video data in a digital mode.
In the NTSC system, a video blanking interval is present between frames in order to discriminate respective frames. A vertical sync signal for distinguishing frames is loaded in the intervals. For the discrimination of lines in a frame, a video blanking interval is present between the lines, loading a horizontal sync signal.
Similarly, in HDTV systems, data blanking interval exists in units of segment and field. This interval contains a data segment sync signal, and a data field sync signal.
FIG. 1 illustrates one segment of data format in accordance with the Grand Alliance HDTV transmission system.
In FIG. 1, a data segment sync signal is loaded in the data blanking interval presented in units of segment, and transmitted from a broadcasting station, without being error-control-code. Here, the compressed video data loaded between the respective data segment sync signals is error-control-coded for transmission.
The data segment sync signal is considered to facilitate recovery of received video data in synchronization.
For this reason, an HDTV recovers the data segment sync signal prior to the complete recovery of the received video data, forming a data symbol clock from the data segment sync signal.
In other words, data corresponding to the data segment sync signal which is not error-control-coded, is loaded in front of the error-control-coded data segment. A receiver detects the data, making the data segment sync signal. Using the clocks in synchronization with the data segment sync signal, a received composite baseband data signal is converted into analog. Accordingly, this implements a synchronous receiving system.
Generally speaking, in a digital transmitting/receiving system, a waveform on which only one symbol is loaded for one symbol period (T) is transmitted so that the receiver side detects the phase of the symbol from the received waveform, recovering the symbol information accurately.
However, as shown in FIG. 2, when the phase of the recovered symbol clock involves an error, the amplitude of the symbol information has an error.
FIG. 3 is a block diagram of an apparatus for recovering the data sync signal and data symbol clock in the Grand Alliance HDTV receiver.
In the aforementioned Grand Alliance HDTV system, four fixed symbol streams are loaded on the video data format as data corresponding to the data segment sync signal for every segment period.
For this reason, in the apparatus of FIG. 3, an A/D converter 1 converts received composite baseband video data into digital. A data segment sync signal detector 2 detects four fixed symbols corresponding to a data segment sync signal from the digital data for every segment period, forming the data segment sync signal for every segment period.
A phase-locked loop 3 uses the data segment sync signal to make a symbol clock in synchronization therewith. The clock is given to A/D converter 1. By doing so, the phase of symbol can be recovered accurately. As noted above, in order for accurate recovery of symbol, a data segment sync signal must be first of all detected precisely.